This invention relates to a laser apparatus and more particularly to apparatus in which metal vapour forms the laser amplifying medium.
Lasers which use metal vapour as the amplifying medium, for example copper or gold vapour, are, typically, of cylindrical geometry and require a high temperature to be maintained in the laser tube within which laser amplification occurs. This high temperature is necessary to maintain the metal vapour at a suitable operating pressure which is typically about one torr as a partial pressure within a buffer gas, which nay have any pressure up to hundreds of torr. For example, in a copper vapour laser, it is necessary to maintain the temperature within the laser tube at about 1600.degree. C. This type of laser may be termed a pure-metal high temperature (PMHT) laser. In presently available copper vapour lasers of the PMHT type, this is achieved by using thermally insulating material around the laser tube so as to reduce heat losses to a minimum and attain the high temperatures required.
Also, in copper vapour lasers, it is current practice to place the thermally insulating material and the laser tube which confines the discharge together within a vacuum envelope.
Thus, where high temperatures are required, there is a large amount of insulating material to be outgassed within the vacuum envelope. The nature and quantity of the thermally insulating materials used at the high temperatures involved make for excessively long outgassing times following exposure to the ambient atmosphere during routine service operations, such as reloading with copper and cleaning the laser windows.
The large amount of thermal insulating materials present both a large thermal capacity and a high thermal impedance, with the result that typical times required for a laser of average power for example, 20 Watts, to attain its operating temperature are about 60-90 minutes.
In another class of metal vapour laser, the amplifying medium is derived from a metal halide which vaporises to form a molecular gas of metal halide at lower temperatures than those required to produce comparable vapour pressures from a solid metal. This type of laser may be termed a metal-halide low temperature (MHLT) laser. When an electrical discharge pulse is passed through the metal halide vapour, the halide dissociates into metal atoms or molecules and halogen atoms or molecules. If a second discharge pulse is then passed before the metal and halogen atoms or molecules can recombine, the metal atoms may be excited to the same energy levels as those which participate in the PMHT laser. For example, in a copper vapour laser, copper bromide may be used. For copper bromide, temperatures in the region of 600-700 degrees C. are sufficient to produce the required partial pressures. However, although these temperatures are relatively low when compared to a laser in which the metal vapour is produced from solid metal, it is still common practice to provide a relatively large mass and volume of thermally insulating material around the laser tube to enable the system to be heated from room temperature to the operating temperature and also to ensure that at the operating temperature, power applied to the amplifying medium is available to the laser process.